Storage subsystems, such as magnetic tape libraries, are widely used for storing information in digital form. Tape storage subsystems typically include one or more tape drives for reading and writing data to removable tape cartridges.
Magnetic tape cartridges have been used to conveniently and efficiently store and handle magnetic recording media for tape drives. One type of tape cartridge consists of a substantially rectangular exterior cartridge housing and a single reel containing a magnetic tape positioned within the housing. The cartridge housing includes an upper housing section and a lower housing section that substantially enclose the magnetic tape. The tape includes a cartridge leader. The cartridge leader becomes exposed through an opening in the cartridge housing during insertion of the cartridge into the tape drive. The tape drive is then able to engage and retrieve the tape from the cartridge for recording and/or playback.
The ability to reliably record and play back data depends upon a constant tape tension to keep the tape in contact with the head and to avoid stretching the tape. This has the effect of moving the data bands apart or closer together thereby making it more difficult to read all of the tracks. As data densities increase the acceptable amount of variation in tension decreases because the tracks are narrower. For future tape drives, being able to monitor and correct the tension will become a necessity.
Previously, tape medium tension was determined by creating loops or bends in the tape medium using swing arms in the tape path. The displacement of the swing arm was inversely proportional to the tension of the tape medium. The additional swing arm component increases complexity. Moreover, the accuracy and sensitivity of a swing arm tension sensor is not reliable.
Therefore, a simple, inexpensive, and accurate way to measure and control tape tension in a tape drive is desired.